Cationic metallocene catalysts based on organoaluminum anions

ABSTRACT

Metallocene catalysts and their preparation and use in the polymerization of olefins. Specifically, the catalysts and processes relate to polymerization of olefins in which an aluminum ionizing agent containing a triphenylcarbenium ion is utilized in preparing the catalyst. The preparation of an olefin polymerization catalyst comprising a metallocene-type catalyst and triphenylcarbenium tetrakis(pentafluorophenyl)aluminate is disclosed.

This application is a continuation-in-part of U.S. patent applicationSer. No. 419,055 filed Oct. 10, 1989, now U.S. Pat. No. 5,155,080 andU.S. patent application Ser. No. 419,057 filed Oct. 10, 1989, nowabandoned.

FIELD OF THE INVENTION

This invention relates, in general, to metallocene catalysts and theirpreparation and use in the polymerization of olefins, and specificallyto a catalyst and a process for preparing catalysts for polymerizationof olefins in which an aluminum ionizing agent containing atriphenylcarbenium ion is utilized in preparing the catalyst.

More specifically, the invention relates to the preparation of an olefinpolymerization catalyst comprising a cationic metallocene andorganoaluminum anion.

BACKGROUND OF THE INVENTION

Alpha olefins, especially propylene, may be polymerized to formpolyolefins in various forms: isotactic, syndiotactic and atactic.Isotactic polypropylene contains principally repeating units withidentical configurations and only a few erratic inversions in the chain.A syndiotactic polymer contains principally repeating units of exactlyalternating stereoisomers. A polymer chain showing no regular order ofrepeating unit configurations is an atactic polymer. In commercialapplications, a certain percentage of atactic polymer is typicallyproduced with the isotactic form.

As disclosed in the relevant art, the structure and properties ofsyndiotactic polypropylene differ significantly from those of isotacticpolypropylene. The isotactic structure for polypropylene is typicallydescribed as having the methyl groups attached to the tertiary carbonatoms of successive monomeric units on the same side of a hypotheticalplane through the main chain of the polymer, e.g., the methyl groups areall above or below the plane. Using the Fischer projection formula, thestereochemical sequence of isotactic polypropylene is described asfollows: ##STR1##

Another way of describing the structure is through the use of NMR.Bovey's NMR nomenclature for an isotactic pentad is . . . mmmm . . .with each "m" representing a "meso" dyad or successive methyl groups onthe same side in the plane. As known in the art, any deviation orinversion in the structure of the chain lowers the degree ofisotacticity and crystallinity of the polymer.

In contrast to the isotactic structure, syndiotactic polymers are thosein which the methyl or other groups attached to the tertiary carbonatoms of successive monomeric units in the chain lie on alternate sidesof the plane of the polymer. Syndiotactic polypropylene is shown inzig-zag representation as follows: ##STR2##

Corresponding representations for syndiotactic polyvinylchloride andpolystyrene, respectively, are: ##STR3##

While it is possible for a catalyst to produce all three types ofpolymers, it is desirable for a catalyst to produce predominantlyisotactic or syndiotactic polymer with very little atactic polymer.Catalysts that produce isotactic polyolefins are disclosed in U.S. Pat.Nos. 4,794,096 and 4,975,403. These patents disclose chiral, stereorigidmetallocene catalysts that polymerize olefins to form isotactic polymersand are especially useful in the polymerization of a highly isotacticpolypropylene.

As described, for example, in the aforementioned U.S. Pat. No.4,975,403, such chiral stereorigid metallocenes may be characterized bythe formula:

    R"(C.sub.5 (R').sub.4).sub.2 MeQ.sub.p                     ( 1)

In formula 1, (C₅ (R')₄) is a cyclopentadienyl or substitutedcyclopentadienyl ring; each R' is the same or different and is ahydrogen or hydrocarbyl radical having 1-20 carbon atoms; R" is astructural bridge between the two (C₅ (R')₄) rings impartingstereorigidity to said catalyst, and R" is selected from the groupconsisting of an alkylene radical having 1-4 carbon atoms, a siliconhydrocarbyl radical, a germanium hydrocarbyl radical, a phosphorushydrocarbyl radical, a nitrogen hydrocarbyl radical, a boron hydrocarbylradical, and an aluminum hydrocarbyl radical: Me is a group 4, 5, or 6metal as designated in the Periodic Table of Elements; each Q is ahydrocarbyl radical having 1-20 carbon atoms or is a halogen; and 0≦p≦3.

Catalysts that produce syndiotactic polypropylene or other syndiotacticpolyolefins are disclosed in U.S. Pat. No. 4,892,851. These catalystsare bridged stereorigid metallocene catalysts. The catalysts have astructural bridge extending between dissimilar cyclopentadienyl groupsand may be characterized by the formula:

    R"(CpRn)(CpR'm)MeQ.sub.p                                   ( 2)

In formula (2), Cp represents a cyclopentadienyl ring; and R and R'represent hydrocarbyl radicals having 1-20 carbon atoms. R" is astructural bridge between the rings imparting stereorigidity to thecatalyst: R'm is selected so that (CpR'm) is a sterically differentsubstituted cyclopentadienyl ring than (CpRn); n varies from 0 to 4 (0designating no hydrocarbyl groups, i.e, an unsubstitutedcyclopentadienyl ring) and m varies from 1-4, MeQ and p are as describedabove with reference to formula (1). The sterically differentcyclopentadienyl rings produce a predominantly syndiotactic polymerrather than an isotactic polymer. Such bridged structures may becharacterized specifically by the foregoing formulas (1) and (2) inwhich R" denotes a structural bridge between the cyclopentadienylgroups. As noted previously, in formula (2), at least onecyclopentadienyl group is substituted in a manner such that the twogroups are sterically different to impart syndiospecificity.Iso-specific structures, as described in the aforementioned patents,U.S. Pat. Nos. 4,794,096 and 4,975,403, can be denoted by a formulasimilar to formula (2) with the exception that the cyclopentadienylgroups (C_(p) R_(n)) and (C_(p) R'_(m)) in formula (2) are the same.

European Patent Application 0 277 003 to Turner et al. (Exxon) relatesto cationic metallocene catalysts prepared by a proton transfer method.A bis (cyclopentadienyl) metal compound containing at least onesubstituent capable of reacting with a proton is combined with a secondcompound having a cation capable of donating a proton and an anionhaving a plurality of boron atoms. For example, the following reactionillustrates the proton transfer procedure:

    Bis (pentamethylcyclopentadienyl) Zirconium dimethyl+7,8-dicarbaundecaborane-->bis (pentamethylcyclopentadienyl) methyldodecahydrido-7,8-dicarbaundecaborato) zirconium+CH.sub.4

European Patent Application 0 277 004 to Turner (Exxon Chemicals) alsorelates to catalysts prepared by a proton transfer method. Abis(cyclopentadienyl) metal compound is combined with a second ioniccompound having a cation that will irreversibly react with a ligand onthe metal compound and an anion having a plurality of lipophilicradicals around a metal or metalloid ion. The following reactionillustrates this procedure:

    tri(n-butyl) ammonium tetra(pentaflurophenyl) boron+bis(cyclopentadienyl) zirconium dimethyl-> C.sub.p2 ZrMe! BPh.sup.f.sub.4 !+CH.sub.4 +tri(n-butyl)N (where Ph.sup.f =pentafluorophenyl).

A by-product of the proton transfer reaction is a Lewis base (amine),some of which can coordinate to the cations and thus inhibit catalystactivity. In the proton transfer reaction, starting materials must bechosen carefully to avoid generating particular amines that can poisoncatalysts. In addition, the catalyst and the polymer produced with thiscatalyst contains undesirable and toxic residual amines.

In most known metallocene catalyst processes, methylalumoxane (MAO) isadded with the metallocene to act as a cocatalyst. MAO functions as analkylating agent which according to one theory of operation alsopromotes ionization of the metallocene catalyst. The cocatalyst canserve as a scavenging agent that reduces basic impurities from thereaction medium which may decrease catalyst activity. MAO is quiteexpensive, and its high cost results in increased costs for any catalystsystem utilizing MAO.

Bis(cyclopentadienyl) complexes in the presence of MAO polymerizeethylene with high efficiency. The metal in such complexes is typicallytitanium, zirconium, or hafnium, but may be any metal from Group 4, 5,or 6 (new notation) of the Periodic Table of Elements. It has beenpostulated that the active catalyst for this type of solubleZiegler-Natta catalyst involves cationic d° alkyl complexes associatedwith a labile stabilizing anion (see Jordan et al., J. Am. Chem. Soc.1986, 108, 7410-7411 and references therein). When employing astereorigid bridged metallocene in conjunction with MAO the resultingcatalyst system can be used to polymerize propylene to highly isotactic,hemiisotactic, or syndiotactic forms of propylene.

As is well known, the soluble metallocene catalyst systems offer severaladvantages over conventional heterogeneous Ziegler-Natta catalystsincluding higher catalyst activities, the production of polymers withnarrow molecular weight distributions, and the synthesis of highlysyndiotactic polymers which are not possible with conventionalcatalysts. It is also well known that high concentrations of MAO arerequired by metallocene catalyst systems which are costly and results ina high polymer ash content requiring additional post-reactor treatmentbefore the polymer can be used.

Group 4 metallocenes in the presence of only trialkylaluminum compoundssuch as R_(n) AlX_(3-n) (where R=alkyl X=halide and n is from 1-3) arenot known to polymerize alpha olefins appreciably with the exception ofmixtures of trimethylaluminum and dimethyl-aluminum fluoride recentlyreported by Zambelli, Longo, and Grassi, "Isotactic Polymerization ofPropene: Homogenous Catalysts Based on Group 4 Metallocenes WithoutMethylalumoxane" Macromolecules 1989, 22, 2186-2189. The presentinvention need not, however, utilize a neutral Lewis acid such asdimethylaluminum fluoride, and the Zambelli et al. disclosure does notcontemplate forming discrete cyclopentadienyl-containing metallocenecations. Furthermore, Zambelli et al. do not contemplatetriphenylcarbenium aluminum ionizing agents as used in conjunction withthe present invention.

The previously mentioned Exxon patent application publication 0 277 004describes a method for preparing base free (C_(p2) Zr(CH₃)! BPh₄ ! typeethylene polymerization catalysts by protonation of a C_(p2) Zr(CH₃)₂methyl group with R₃ NH! BPh₄ ! in hydrocarbon solvent. The Exxonapplication describes the use of BPh^(f) ₄ ! as a counterion with astereorigid bridged cationic metallocene for the production of isotacticpolypropylene. BPh^(f) ₄ ! is equivalent to B(C₆ F₅)₄ wherein the phenylgroups are fully and completely fluorinated. The Exxon application doesnot disclose aluminum ionizing agents, however, and there is no teachingor indication of any triphenylcarbenium aluminum ionizing agents in theExxon '004 patent application.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a cationicmetallocene cayalyst characterized in accordance with formula (4) belowand a process for the preparation of a cationic metallocene catalyst.Furthermore, this invention relates to a process for the polymerizationof alpha olefins by providing a cationic metallocene catalyst preparedby the reaction of a neutral metallocene ligand containing at least onesubstituent capable of reactions with a carbenium ion and atriphenylcarbenium aluminim ionizing agent.

In carrying out the invention there is provided a neutral metallocenecharacterized by the formula:

    (Cp') (Cp") MQ.sub.k                                       ( 3)

Each of Cp' and Cp" is a cyclopentadienyl or a hydrocarbyl substitutedcyclopentadienyl group. Cp' and Cp" are the same (as in formula 1 above)or different (as in formula 2 above) and they may be bridged as in bothformulas (1) and (2) or they may be unbridged. M is Group 4, 5 or 6metal and Q is a hydride, a halogen, or a hydrocarbyl radical. Each Q isthe same or different, except only one Q is a hydride and k is from 2 to3.

Unbridged metallocenes in which the cyclopentadienyl rings are free torotate about their coordination axes can, as indicated previously, beused in the polymerization of ethylene. Stereorigid metallocenestructures such as the bridged isospecific or syndiospecific structuresdepicted specifically by formulas (1) and (2) above may, of course, beused in the polymerization of C₃₊ alpha olefins, particularly propylene.In each of these cases, the neutral metallocene structure may be reactedwith a triphenylcarbenium aluminum ionizing agent as indicated below toproduce a cationic metallocene catalyst depicted by the formula:

     (Cp')(Cp")MQ.sub.L !.sup.+   AlR"'.sub.4 !.sup.-          ( 4)

Here, Cp', Cp", M and Q are as described previously, L is 1 or 2, andR"' is an aklyl, a hydride, a halogen, an alkoxy, aryloxy, an aryl groupor substituted aryl group, each R"' being the same or different, exceptonly one R"' is a hydride.

The neutral metallocene may be substituted with several differentgroups, including but not limited to hydrocarbons such as methyl groupsand/or other ring structures. The resulting cationic metallocenecatalysts may comprise Cp groups that are the same or different. If theCp groups are the same, the resulting cationic metallocene catalysts canbe used to produce isotactic polymer product. If the Cp groups aredifferent, the resulting cationic metallocene catalysts can be used toproduce syndiotactic polymer product. The specific groups substituted onthe cyclopentadienyl rings thus can be determinative of whether theresulting cationic metallocene catalyst produces isotactic, syndiotacticor atactic polymer product.

The cyclopentadienyl groups may be and probably are bridged to provideisospecific or syndiospecific catalysts. Thus, it will be understoodthat the formula, (Cp') (Cp") MQ_(k) is inclusive of metallocene ligandstructures which are substituted in a manner to provide a structuralbridge between the cyclopentadienyl groups prior to reaction with thetriphenylcarbenium ionizing agent to form the ionic complex.

The present invention involves the use of a discrete aluminum ionizingagent useful as a polymerization catalyst when combined withmetallocenes. In a preferred embodiment of the invention thetriphenylcarbenium aluminum ionizing agent is triphenylcarbeniumtetrakis(pentafluorophenyl)aluminate. Furthermore, in the preparation ofa cationic metallocene catalyst in accordance with an embodiment of theinvention there is employed a neutral metallocene precursor comprising astereorigid metallocene characterized by a metallocene ligand having twosterically similar or dissimilar ring structures joined to acoordinating transition metal atom. The ring structures may or may notcomprise substituted or unsubstituted cyclopentadienyl groups in astereorigid relationship relative to the metal atom. In furtherembodiments of the present invention, a structural bridge may extendbetween similar or dissimilar ring structures as described above.

The neutral metallocene may comprise a first cyclopentadienyl ringstructure that is substituted or unsubstituted and a secondcyclopentadienyl ring structure which is substituted and stericallydifferent from the first ring structure.

The present invention makes MAO unnecessary in some cases, but there maybe MAO present in the reaction. The present invention further involvesthe use of a trialkylaluminum compound in conjunction with an aluminumionizing agent to alkylate and ionize the neutral metallocene and reactwith basic impurities present in the reaction medium.

In carrying out the invention, a neutral metallocene is provided inreaction with a triphenylcarbenium aluminum ionizing agent andtrialkylaluminum. The neutral metallocene and the triphenylcarbeniumaluminum ionizing agent are contacted under conditions that causeionization of the metallocene by the triphenylcarbenium aluminumionizing agent thereby forming an ion pair in which the metallocene hascatalytic activity for the polymerization of olefins. More specifically,a trialkylaluminum is employed under conditions that cause alkylation ofthe metallocene in conjunction with ionization by the triphenylcarbeniumionizing agent. The neutral metallocene in the process is characterizedby the presence of at least two cyclopentadienyl or substitutedcyclopentadienyl groups which may be connected through a bridging group,and coordinated with a metal atom from Group 4, 5, or 6 (new notation)of the Periodic Table of Elements, and having at least two other groups(referred to here as Q groups) coordinated to the metal, which groupsmay be a hydride, a halogen, an amide, or a hydrocarbyl radical. Thepreferred metal is a Group 4 metal, and most preferably zirconium,although titanium, hafnium and Group 5, and 6 metals may also be used. Apreferred embodiment of the present invention uses a group comprisingchlorine, although other groups may be used as well.

The ionized metallocene is characterized by an aluminum anion groupAlR"'₄, which is not coordinated or is only loosely coordinated with themetallocene cation, and is chemically unreactive with the cation. Themetallocene cation contains at least one Q group as described above andpreferably a hydride or a hydrocarbyl radical. In the preferredembodiment of the invention it is contemplated that the catalyst will beused to polymerize propylene, although ethylene, styrene, and othermonomers may be polymerized with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is particularly applicable to bridged stereo-rigidmetallocene ligands which are especially suitable in the polymerizationof alpha olefins to produce stereo-specific polymers, for example,isotactic and syndiotactic polypropylene. It is also applicable tometallocene ligands in which the cyclopentadienyl groups are notbridged. Both bridged and unbridged metallocenes are known in the art tobe useful in the polymerization and copolymerization of ethylene toproduce polyethylene and co-polymers such as ethylene-propyleneco-polymers. With respect to bridged stereo-rigid metallocene ligands,they may be the same or different to produce isotactic or syndiotacticpolymers. By way of example, chiral ethylene bridged bis (indenyl)metallocene structures are useful in the catalysis of polymerizationreactions leading to isotactic polypropylene whereas bridged ligandstructures such as isopropyl (cyclopentadienyl) (fluorenyl) metalloceneligand structures are useful as catalysts in the production ofsyndiotactic polypropylene. For a description of other metallocenestructures to which the present invention may be applied, reference ismade to European Patent Application Publication No. 0423100A2 publishedApr. 17, 1991, the entire disclosure of which is incorporated byreference.

Catalysts employing stereorigid cationic metallocene catalyst systemswithout MAO polymerize propylene with high efficiency yielding polymerswith low ash content. However, catalyst stereospecificity is reducedrelative to the MAO based catalyst when certain metallocenes are pairedwith --BPh^(f) ₄, resulting in polymers of lower crystallinity. Suchpolymers are less desirable. This is especially true for thesyndiospecific metallocene iPr C_(p) (Flu)!ZrCl₂ (whereiPr=isopropylidene interannular bridge and Flu=fluorenyl group).

The present invention provides an alternative anion for use inmetallocene reactions that will not adversely affect the stereochemistryof the catalyst. The aluminum ionizing agent of the present inventionprovides a new aluminum-based metallocene catalyst and process.

The present invention relates to a discrete aluminum ionic compounduseful as a polymerization catalyst when combined with metallocenes, amethod of preparing catalysts, and a process for using the catalysts forthe polymerization of olefins. A preferred specific application of theinvention relates to the use of triphenylcarbeniumtetrakis(pentafluorophenyl)aluminate Ph₃ C! AlPh^(f) ₄ ! as an ionizingagent. When combined with certain stereorigid metallocenes, for example,syndiospecific iPr C_(p) (Flu)!ZrCl₂, the resulting metallocene cation-aluminum anion pair provides higher crystallinity polymers than thoseobtained with cationic metallocenes derived from boron-containing anionssuch as --BPh^(f) ₄. Furthermore, the catalysts have the advantage ofrequiring a lower total Al/Zr mole ratio than the MAO based catalysts.

In "Polyfluoroaryl Organometallic Compounds, Part IV. FluorocarbonDerivatives of Tricovalent Aluminum", J. Chem. Soc. (C), 1967, p. 2185by Chambers and Cunningham, it was reported that the formation of awhite solid residue resulting from an anionic aluminum compound wassynthesized by the reaction of pentafluorophenyl-lithium with aluminumtribromide in hydrocarbon solvents. Chambers and Cunningham reported theformation of white solid residue containing pentafluorophenyl but couldnot extract any single lithium-aluminum species with a variety ofsolvents.

The present invention goes far beyond the activity described in theChambers article in that the inventors in the present case have isolateda triphenylcarbenium aluminum compound, and have shown that such acompound is useful in the polymerization of alpha olefins.

In carrying out the invention there is provided a neutral metallocenecharacterized as described previously by the formula:

    (Cp') (Cp") MQ.sub.k                                       (3)

wherein Cp', Cp", MQ, and k are as described above. More specific andpreferred neutral metallocenes are bridged metallocenes as characterizedby formulas (1) and (2) above. In addition there is provided atriphenylcarbenium aluminum ionizing agent which does not contain anactive proton. The ionizing agent is characterized by the formula:

     Ph.sub.3 C!  AlR"'.sub.4 !                                (5)

In formula (5) Ph is a phenyl group or a substituted phenyl group. R"'may be a hydride, a halogen, or a hydrocarbyl radical, more specificallyan alkyl or aryl group or an akloxy, aryloxy, or substituted aryl group,each R' being the same or different, except only one R"' is a hydride.

The neutral metallocene and aluminum ionizing agent are contacted underconditions to cause ionization of the neutral metallocene by theionizing agent to form an ion pair comprising a metallocene cationhaving catalytic activity in olefin polymerization and an AlR"'₄ anion,the latter being not coordinated or only loosely coordinated to themetallocene cation and, chemically unreactive with the metallocenecation. Where R"' is a halogen the metallocene is alkylated with atrialkylaluminum such as TEAL.

In a preferred embodiment of the present invention, a cyclopentadienylmetal compound, in which the metal is selected from Group 4, 5 or 6 ofthe Periodic Table of Elements, said compound containing a Q group whichis a hydride, halogen, amide, or hydrocarbyl radical, is combined with atriphenylcarbenium aluminum ionizing agent and trialkylaluminumalkylating agent. The triphenylcarbenium aluminum ionizing agent doesnot contain an active proton and when combined, the neutral metallocenecompound is ionized by the triphenylcarbenium aluminum ionizing agent toform an ion-pair in which the metallocene cation has catalytic activityfor the polymerization of an olefin.

Furthermore, the AlR"'₄ anion, which is not coordinated or is onlyloosely coordinated to the metallocene cation, is chemically unreactivewith the metallocene cation. The transition metal of the metallocene ispreferably selected from the group consisting of zirconium, hafnium andtitanium with zirconium being most preferred followed by hafnium andtitanium, respectively. However, as noted previously, it is contemplatedthat other metals of Groups 5 and 6 of the periodic table may serve inthe present invention.

In a particularly preferred embodiment of the present invention, iPrC_(p) (Flu)!ZrCl₂ is utilized in the preparation of the catalyst and iscontacted with triethylaluminum and Ph₃ C! AlPh^(f) 4! in toluenesolution. These components will be combined at a temperature within therange from about 0° C. to about 50° C. The components will be combined,preferably, in an aromatic hydrocarbon solvent, most preferably toluene.Nominal holding times within the range of from about ten seconds toabout sixty minutes will be sufficient to produce the preferred catalystof this invention.

In a further aspect of the invention, the catalyst, immediately afterformation, is used to polymerize an olefin, particularly ethylene orpropylene and most preferably propylene, at a temperature within therange from about 0° C. to about 100° C. and at a pressure within therange from about 25 to about 600 psig. It will be understood that othermonomors besides propylene and ethylene may be polymerized using thecatalyst of the present invention, and this disclosure should not beconstrued as limiting polymerization to any particular polymer ormonomer.

Having thus broadly described the present invention and the preferredembodiments thereof, reference is made to the following experimentalwork to further characterize the invention. It will be appreciated thatthe experimental work should not be construed as limiting the invention.The aluminum and metallocene reagents used in the examples were eitherpurchased or prepared following published techniques or proceduresdescribed below.

Experimental work respecting the present invention was carried outemploying syndiospecific and isospecific metallocenes with two differenttriphenylcarbenium ionizing agents, (Ph₃ C)(AlPh^(f) ₄) and (Ph₃C)(BPh^(f) ₄), and with methylalumoxane. The results of thisexperimental work are set forth in Tables I and II below. The followingExample illustrates the preparation of a preferred triphenylcarbeniumionizing agent, (Ph₃ C)(AlPh^(f) ₄) used in the experimental work.

EXAMPLE 1

16 mmol of bromopentafluorobenzene were diluted with 60 mL of toluene,cooled to -78° C., and one equivalent of butyllithium (1.6M solution inhexane) was added slowly. Pentafluorophenyllithium precipitated as awhite solid during the reaction. After stirring for 2 hrs. at -78° C., 4mmol of AlBr₃ dissolved in 15 mL of toluene were added slowly. Thereaction mixture was cautiously warmed to room temperature and 4 mmol oftriphenylmethyl chloride dissolved in 20 mL of methylene chloride wereadded resulting in an orange slurry. After filtration, solvents wereremoved from the filtrate in vacuo and the orange residue was thoroughlytriturated with pentane. The resultant moderately air sensitive yellowsolids were collected on a closed filter and washed for 12 hrs. withboiling hexane in an extraction assembly. The yield was 2.45 g of brightyellow powder (65%). The calculated wt parts for C₄₃ H₁₅ F₂₀ Al are: C,54.81; H, 1.62. The amounts found by elemental analysis are: C, 51.97;H, 1.62 The molecular structure is characterized by the following NMRdata presented in standard notation: H-NMR (CD₂ Cl₂); chemical shifts inppm: 8.26 (t, 1H), 7.87 (t, 2H), 7.66 (d, 2H). F-NMR (CD₂ Cl₂), relativeto C₆ F₆ @ -163.7 ppm int. ref.:-123.6 (2 F), -159.4 (1 F), -165.5 (2F).

The following Examples 2 and 3 are illustrative of polymerizationprocedures carried out with the preferred triphenylcarbeniumtetrakis(pentafluorophenyl)aluminate ionizing agent, (Ph₃ C)(AlPhf₄),and alumoxane, both used in conjunction with a syndiospecificmetallocene.

EXAMPLE 2

5.2 mL of a 0.15M triethylaluminum (TEAl) solution in hexane were addedto 1.3 mg of iPr C_(p) (Flu)ZrCl₂ slurried in 10 mL of toluene giving abright yellow solution. The metallocene solution was added to a dry twoliter jacketed autoclave equipped with a magnedrive stirrer followed by1,000 mL of propylene. The polymerization was initiated by adding 5.6 mgof Ph₃ C! AlPh^(f) ₄ ! as a toluene solution (10 mL) with 400 mL ofpropylene at room temperature. The catalyst was prepolymerized onheating the reactor, with stirring, to the reaction temperature (60° C.)within five minutes of Ph₃ C! AlPh^(f) ₄ ! addition. The polymerizationwas terminated by venting all unreacted monomer. If the yield was lessthan 50 g, toluene was added to the reaction products and thepolymer/toluene slurry was washed with a 50/50 methanol/4N HCl solutionand then water. The aqueous layer was separated and toluene was removedfrom the polymer with a rotoevaporator.

EXAMPLE 3

0.5 mg of iPr Cp(Flu)!ZrCl₂ were dissolved in 5.0 mL of a 10 wt %methylalumoxane (MAO) solution in toluene and added to a 40 mL stainlesssteel bomb equipped with ball valves on each end. The average molecularweight of the MAO was about 1,100 grams per mole. The catalyst solutionwas charged to a 2 liter autoclave reactor which contained 1 liter ofpropylene at room temperature. The catalyst was prepolymerized onheating the reactor contents, with stirring, to reaction temperature(60° C.) within five minutes after charging. The polymerization wasterminated by venting all unreacted monomer. If the yield was less than50 g, toluene was added to the reaction products and the polymer/tolueneslurry was washed with a 50/50 methanol/4N HCl solution and then water.The aqueous layer was separated and toluene was removed from the polymerwith a rotoevaporator.

The results of experimental work carried out employing thesyndiospecific metallocene, isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride, are set forth in Table I. The resultsof the experimental work carried out employing the isospecificmetallocene, ethylene bis(indenyl) zirconium dichloride, are presentedin Table II. In each of Tables I and II, the quantities of metallocene,of the appropriate catalyst component A as designated in the Table, andof TEAL are shown in the first, second and third columns, respectively.The reaction temperature and time are shown in the fourth and fifthcolumns, respectively, and the polymer yield in the sixth column. Theintrinsic viscosity and melting point are shown in the seventh andeighth columns, respectively and the percent of racemic (Table I) ormeso (Table II) pentads for the polymer products is shown in the lastcolumn of each Table.

                                      TABLE I                                     __________________________________________________________________________    SYNDIOSPECIFIC iPr Cp(Flu)!ZrCl.sub.2                                         PROPYLENE POLYMERIZATION RESULTS.sup.a)                                       Zirconocene,                                                                            TEAL,       Yield,                                                                             n!,.sup.b)                                                                      m. pt.,.sup.c)                                   mg    A, mg                                                                             mmol                                                                              T, °C.                                                                     t, min.                                                                           g   dl/g                                                                             °C.                                                                        rrrr, %                                      __________________________________________________________________________    A =  Ph.sub.3 C! AlPh.sub.4.sup.f !                                           5.0   40.0                                                                              2.00                                                                              50  60  100 1.24                                                                             138 83.7                                         1.0   9.0 2.00                                                                              50  30  15  1.05                                                                             138                                              1.3   6.0 0.78                                                                              60  60  14     142                                              1.3   11.2                                                                              0.78                                                                              60  70  48  1.17                                                                             139                                              1.3   16.8                                                                              0.78                                                                              60  60  22     141                                              A =  Ph.sub.3 C! BPh.sub.4.sup.f !                                            0.5   6.0 0.66                                                                              50  60  56  1.12                                                                             129 80.0                                         0.5   6.0 2.00                                                                              50  60  47  1.13                                                                             131 79.0                                         A = MAO                                                                       0.5   450 0.00                                                                              50  60  39     140 85.8                                         0.5   450 0.00                                                                              60  60  138 1.29                                                                             136                                              __________________________________________________________________________     .sup.a) 1400 mL of liquid propylene.                                          .sup.b) Intrinsic viscosity; determined from 135° C.                   decahydronapthalene solutions.                                                .sup.c) DSC melting points of samples previously heated to 450K, held at      this temperature for 5 minutes, and cooled at 10K/min with baseline           correction.                                                                   .sup.d) .sup.13 CNMR results for 20% (w/w) polymer solutions in               1,2,4trichlorobenzene/d.sub.6Benzene.                                    

                                      TABLE II                                    __________________________________________________________________________    ISOSPECIFIC Et Ind!.sub.2 ZrCl.sub.2                                          PROPYLENE POLYMERIZATION RESULTS.sup.a)                                       Zirconocene,                                                                            TEAL,       Yield,                                                                             n!,.sup.b)                                                                      m. pt.,.sup.c)                                                                    mmmm,.sup.d)                                 mg    A, mg                                                                             mmol                                                                              T, °C.                                                                     t, min.                                                                           g   dl/g                                                                             °C.                                                                        %                                            __________________________________________________________________________    A =  Ph.sub.3 C! AlPh.sub.4.sup.f !                                           5.0   40.0                                                                              2.00                                                                              50  60  56  0.57                                                                             140 86.5                                         1.3   11.2                                                                              0.78                                                                              60  60  24  0.63                                                                             141 85.8                                         A =  Ph.sub.3 C! BPh.sub.4.sup.f !                                            0.6    5.6                                                                              0.78                                                                              60  30  27  0.49                                                                             135 85.5                                         A = MAO                                                                       1.0   450 0.00                                                                              60  30  97  0.51                                                                             135 85.5                                         __________________________________________________________________________     .sup.a) 1400 mL of liquid propylene.                                          .sup.b) Intrinsic viscosity; determined from 135° C.                   decahydronapthalene solutions.                                                .sup.c) DSC melting points of samples previously heated to 450K, held at      this temperature for 5 minutes, and cooled at 10K/min with baseline           correction.                                                                   .sup.d) .sup.13 CNMR results for 20% (w/w) polymer solutions in               1,2,4trichlorobenzene/d.sub.6Benzene.                                    

From an examination of the data in the foregoing Tables I and II, it canbe seen that catalyst activity with the aluminum ionizing agent is lowerthan the activity relating to the use of MAO or boron ionizing agents.Also, it will be recognized that the identity of the catalyst component,whether it be aluminum, boron, or MAO has little effect on intrinsicviscosity. The intrinsic viscosity is noted by the quantity n! as setforth in Table I and Table II. In general, it is desirable for theintrinsic viscosity of the polymer product to be about one dl/g orhigher.

The experimental work reported in Table I and Table II indicates thataluminum containing ionizing agents produce polymers that are morecrystalline, and more stereoregular than boron. The crystallinity of thepolymer is indicated by the melting point figures in Table I and TableII. It can be seen that, in general, the runs with an aluminum basedcatalyst component in Table II show a higher melting point, and acorrespondingly higher crystallinity, than catalyst components producedwith the boron ionizing agent or with MAO. With regard to thesyndiospecific results in Table I, the same general relationship isobserved.

Having described specific embodiments of the present invention, it willbe understood that modifications thereof may be suggested to thoseskilled in the art, and it is intended to cover all such modificationsas fall within the scope of the appended claims.

We claim:
 1. In a process for the preparation of a cationic metallocenecatalyst, the steps comprisinga) providing a neutral metallocene olefinpolymerization catalyst precursor containing at least one substituentcapable of reacting with a carbenium ion; b) providing atriphenylcarbenium aluminum ionizing agent which does not contain anactive proton and is characterized by the formula (Ph₃ C)(AlR"'₄),wherein Ph is a phenyl group or a substituted phenyl group, R"' is analkyl, a hydride, a halogen, an alkoxy, an aryloxy, an aryl group or asubstituted aryl group, each R"' being the same or different, providedthat no more than one R"' is a hydride; c) providing a trialkylaluminum; and d) contacting together said neutral metallocene, saidtrialkyl aluminum and said triphenylcarbenium aluminum ionizing agentunder conditions to cause alkylation and ionization of said neutralmetallocene by said triphenylcarbenium aluminum ionizing agent to forman ion pair comprising a metallocene cation having catalytic activity inolefin polymerization and an AlR"'₄ anion, which is chemicallyunreactive with the metallocene cation.
 2. The process of claim 1,wherein said neutral metallocene is in the form of a stereorigidmetallocene characterized by a metallocene ligand having two stericallyidentical or non-identical ring structures joined to a coordinatingtransition metal atom, each of said ring structures being a hydrocarbylsubstituted or unsubstituted cyclopentadienyl group and in a stereorigidrelationship relative to said coordinating transition metal atom toprevent rotation of said ring structure about said metal atom.
 3. Theprocess of claim 2, wherein said neutral metallocene is characterized bya structural bridge extending between said identical or non-identicalring structures.
 4. The process of claim 3, wherein said neutralmetallocene comprises a first cyclopentadienyl ring structure which issubstituted with a hydrocarbyl group or unsubstituted and a secondcyclopentadienyl ring structure which is substituted with a hydrocarbylgroup and which is sterically different from said first cyclopentadienylring structure.
 5. The method of claim 4, wherein the transition metalof said neutral metallocene is a Group IV or Group V metal from thePeriodic Table of Elements.
 6. The method of claim 5, wherein saidtransition metal is titanium, zirconium or hafnium.
 7. In a process formaking a cationic metallocene catalyst, the steps comprisinga) providinga neutral metallocene characterized by the formula:

    (Cp') (Cp") MQ.sub.k

wherein:Cp' and Cp" are each a cyclopentadienyl or a hydrocarbylsubstituted cyclopentadienyl group and are the same or different, M is aGroup 4, 5, or 6 metal, Q is a hydride, a halogen, or a hydrocarbylradical, each Q being the same or different, except only one Q can be ahydride and k is from 2 to 3; b) providing a triphenylcarbenium aluminumionizing agent which does not contain an active proton and ischaracterized by the formula:

     Ph.sub.3 C! AlR"'.sub.4 !

wherein: Ph is a phenyl group or a substituted phenyl group, R"' is analkyl, a hydride, a halogen, an alkoxy, an aryloxy, a hydrocarbylradical, an aryl group or substituted aryl group, each R"' being thesame or different, except only one R"' is a hydride; c) providing atrialkyl aluminum; and d) contacting together said neutral metallocene,said trialkyl aluminum and said triphenylcarbenium aluminum ionizingagent under conditions to cause alkylation and ionization of saidneutral metallocene by said triphenylcarbenium aluminum ionizing agentto form an ion pair comprising a metallocene cation having catalyticactivity in olefin polymerization and an AlR"'₄ anion, which ischemically unreactive with the metallocene cation.
 8. A process asrecited in claim 7, wherein M is a Group IV metal chosen from the groupconsisting of titanium, zirconium and hafnium.
 9. A process as recitedin claim 8, wherein M is hafnium.
 10. A process as recited in claim 8,wherein M is zirconium.
 11. A process as recited in claim 10, whereineach Q is a a hydride or hydrocarbyl radical.
 12. A process as recitedin claim 11, wherein each R"' is a pentafluorophenyl group.
 13. Themethod of claim 7, wherein the ion pair produced in step (c) ischaracterized by the formula:

     (Cp')(Cp") MQ.sub.L !.sup.+   AlR"'.sub.4 !.sup.-

wherein: Cp', Cp", Q, and R"' are as defined in claim 8; L is 1 or 2;and the AlR"'₄ ⁻ anion is chemically unreactive with the metallocenecation.
 14. A process for the polymerization of alpha olefinscomprisinga. providing a cationic metallocene catalyst prepared by theprocess of contacting together a neutral metallocene olefinpolymerization catalyst precursor containing at least one substituentcapable of reacting with a carbenium ion, a triphenylcarbenium aluminumionizing agent which does not contain an active proton and ischaracterized by the formula (Ph₃ C)(AlR"'₄), wherein Ph is a phenylgroup or a substituted phenyl group, R"' is an alkyl a hydride, ahalogen, an alkoxy, an aryloxy, an aryl group or a substituted arylgroup, each R"' being the same or different, provided that no more thanone R"' is a hydride; and a trialkyl aluminum under conditions to causealkylation and ionization of said neutral metallocene by saidtriphenylcarbenium aluminum ionizing agent to form an ion paircomprising a metallocene cation having catalytic activity for olefinpolymerization and an AlR"'₄ anion which is not coordinated to themetallocene cation and is chemically unreactive with the metallocenecation; and b. contacting said catalyst in a polymerization reactionwith an alpha olefin under polymerization conditions to producepolymerization of said alpha olefin.
 15. The process of claim 14 whereinsaid metallocene is a stereorigid metallocene characterized by ametallocene ligand having two sterically similar or dissimilar ringstructures which are sterically the same or different joined to acoordinating transition metal atom, each of said ring structures being ahydrocarbyl substituted or unsubstituted cyclopentadienyl group and in astereorigid relationship relative to said coordinating transition metalatom to prevent rotation of said ring structure about said metal atom.16. The process of claim 15 wherein said metallocene is characterized bya structural bridge extending between said same or different ringstructure.
 17. The process of claim 16 wherein said a metallocene of aGroup IV metal selected from the group consisting of titanium,zirconium, and hafnium.
 18. The process of claim 17 wherein said alphaolefin is propylene.
 19. The process of claim 18 wherein said Group IVmetal is zirconium.
 20. A metallocene catalyst comprising a cationicmetallocene characterized by the formula:

     (Cp')(Cp") MQ.sub.L !.sup.+   AlR"'.sub.4 !.sup.-

wherein Cp' and Cp" are each a cyclopentadienyl or a hydrocarbylsubstituted cyclopentadienyl group and are the same or different, M is aGroup 4, 5, or 6 metal, Q is a hydride, or a hydrocarbyl radical, each Qbeing the same or different, except only one Q is a hydride, L is 1 or2, R"' is an alkyl, a hydride, a halogen, an alkoxy, aryloxy, ahydrocarbyl radical, an aryl group or substituted aryl group, each R"'being the same or different, except only one R"' is a hydride, preparedby the process of contacting together a neutral metallocenecharacterized by the formula:

    (Cp') (Cp") MQ.sub.k

wherein Cp' and Cp", M and Q are each as defined above and k is from 2to 3, a triphenylcarbenium aluminum ionizing agent which does notcontain an active proton and is characterized by the formula:

     Ph.sub.3 C)!  AlR"'.sub.4 !

wherein Ph is a phenyl group or a substituted phenyl group and R"' is asdefined above, and a trialkyl aluminum, under conditions to causealkylation and ionization of said neutral metallocene by saidtriphenylcarbenium aluminum ionizing agent.
 21. A catalyst as recited inclaim 20 wherein M is a Group IV metal chosen from the group consistingof titanium zirconium, and hafnium.
 22. A catalyst as recited in claim21 wherein R"' is a phenyl or substituted phenyl group.
 23. A catalystas recited in claim 22 wherein R"' is pentafluorophenyl group.
 24. Acatalyst as recited in claim 20 wherein M is zirconium.
 25. A catalystas recited in claim 20 wherein Q is a alkyl group.
 26. A catalyst asrecited in claim 25 wherein R"' is a pentafluorophenyl group.
 27. Acatalyst as recited in claim 26 wherein L is
 1. 28. In a process for thepolymerization of alpha olefins comprising contacting the metallocenecatalyst of claim 27 with an alpha olefin under polymerizationconditions.